Japanese laid-open patent publication No. 2007-295773 discloses a hand-held power tool which is capable of controlling output torque of a tool bit driven by a motor. This power tool is constructed to tighten a screw by giving impact in the circumferential direction and rotation to the tool bit in the form of a screw bit.
In the known screw tightening machine, however, by provision of the construction in which rotation and impact are given to the tool bit, it is likely to have a complicated device configuration by any means.